I've compiled a list of every DT (4-3 DTs, 3-4 NTs, and 3-4 DEs) that has played in the past 5 years. Using PFF ratings for each one, I have done a couple things:

Charted average rating with years played:

As you can see, DTs have a small bump in skill in year 2, but don't really seem to have a large change until year 7. After 11 years, they are typically done. I don't know what happens in year 9.

Charted number of players in the league with years played:

The vast majority of DTs are in their first 4 years. This is totaled over 5 years, so to get the average number of players per year, divide by 5.

Charted total rating over the past 5 years with draft position (the clump at the end is UDFAs):

This looks like a bunch of nonsense. I'm hoping that comparing this with other positions (and maybe with some smoothing) will yield some meaningful results.

Cool note: The biggest bust by far is Tyson Jackson. His -43.8 is the 3rd lowest rating of all 395 players that have played in the last 5 years. The 2 guys worse than him were drafted 81st (Roy Miller, -47.1) and 152nd (Antonio Johnson, -46.8). Jackson, as you know, was drafted 3rd.

The best value? No one has been as good as Justin Smith (+169). He was drafted 4th, though. Geno Atkins wasn't drafted until the 120th pick, and has a rating of +125.4.

Anyway, I'm planning on doing all positions, I decided to do DTs first, what with Star coming out and all. I'll post the other positions here as well if people are interested. If not, I'll keep it all to myself.

Defensive tackles very rarely pan out in free agency. I wonder if some of those spikes are due to contract years.

That and the fact that most guys that suck badly don't see 7 years.

By the time you hit a guy in his 7th year in the league, he's at about 29 yrs old so he's still as physically strong as he was. He's also been a good enough player to hang around 7 years and so he's been able to learn as he's been in the league.

After the 7 year mark you're finding guys that are in their 30s and starting to break down (because DTs are heavy and it's hard on their bodies).

By the time you hit a guy in his 7th year in the league, he's at about 29 yrs old so he's still as physically strong as he was. He's also been a good enough player to hang around 7 years and so he's been able to learn as he's been in the league.

After the 7 year mark you're finding guys that are in their 30s and starting to break down (because DTs are heavy and it's hard on their bodies).

It's probably selection bias as much as anything.

Yeah, that's why I included the number of players for each year as well. There are twice as many rookies playing as there are 7th year guys.

May I propose an alternative analysis, magichef? I'm not sure if you have the data to do this or not.

My theory is that there are two reasons to see increases in performance over time (prior to Father Time's inevitable emasculation). First, you have the normal factor of guys gaining more experience and getting more savvy. This is what we think we're seeing in your graph.

However, I think there's another factor in play as well, which is mildly disturbing given your results. I think that the guys who are in their 3rd or 5th or 8th year are likely to be better players overall than the guys in their 1st or 2nd year. They have more innate talent or better work ethics or are smarter or whatever. You have lots of guys who barely make a roster, play a year or two, and then wash out. The guys still playing in Year 7 are better players in general or they wouldn't have survived.

So what this means is that, even if there was no benefit of added experience, your graph should show an increase in performance related to years of experience. This disturbs me because the increase in your graph is somewhat shallow for the first seven years, which probably covers the entire careers of a vast majority of players.

What does this mean? It could possibly mean that there is no real benefit of experience. If you're good, you're good, and the increase we see with added years of tenure is the simple fact that the weaker players are being weeded out of the analysis pool as time goes on.

An alternative analysis would look at each player, and their rankings in their 1st year in the league, 2nd year, and so on. If you want to look at the trend over the first ten years of a player's career, you only examine players with ten years of experience and look at each year of development.

You said you only have five years of data, but I think that would be sufficient. I suspect that most of the benefit of experience occurs in that time frame anyway.